In order to maintain clean a semiconductor wafer (hereinafter referred to as “wafer”), for example, manufacturing steps for a semiconductor device include a step for cleaning the wafer according to need, in each manufacturing step and before or after a certain step.
In accordance with a finer circuit pattern, it is necessary to clean a rear surface of the wafer, for coping with a defocus. The defocus is a phenomenon in which a pattern becomes out of focus upon exposure because of a warp of a wafer. The defocus may occur, for example, when the wafer is exposed in such a manner that particles adhering on a rear surface of the wafer remain between a stage on which the wafer is placed and the wafer.
As to a cleaning method of the rear surface of the wafer, Patent Document 1 proposes a technique in which a rear surface of a substrate is supported and held, and the rear surface of the substrate is cleaned by a brush. In this method, the substrate is transferred between a first substrate holding unit for holding a peripheral zone in the rear surface of the substrate, and a second substrate holding unit for holding a central zone in the rear surface of the substrate. Thus, the whole rear surface of the substrate can be cleaned. In addition, the method requires no space for reversing the substrate, a size of an apparatus can be reduced.
However, as a wiring has recently become finer due to a technique such as a liquid immersion exposure and a double patterning, the number of steps included in the manufacturing steps of a semiconductor device increases. Thus, particles are more likely to adhere on a rear surface of a wafer, whereby improvement in detergency is further required. In addition, further enlargement of a wafer size, i.e., a diameter from 300 mm to 450 mm is under review, but an apparatus that is small in size as much as possible is preferred. In order thereto, it is under review that a plurality of brushes are used in one cleaning apparatus to improve detergency, while a size of the apparatus is reduced.
Patent Document 2 proposes a structure in which, when an upper surface of a substrate is cleaned by two cleaning brushes attached to one support arm while the substrate is rotated about a vertical axis, a distal end block of the support arm is formed into an arcuate shape and is rotated about the vertical axis. Since this method is for cleaning an upper surface of a substrate, it is necessary to move the cleaning brush through a rotational center of the substrate to reach an outer peripheral part thereof, in order to clean a central zone of the substrate. Since a driving mechanism of the support arm is located outside a cup surrounding a circumference of the substrate, a turning radius of the support arm supporting the cleaning brush is larger than a radius of the substrate. Thus, it is difficult to reduce a size of the apparatus. Moreover, since the cleaning brush moves through the rotational center of the substrate up to the outer peripheral part thereof, a moving distance of the cleaning brush is long, which elongates a process time.
Patent Document 3 proposes a technique for cleaning a substrate surface with the use of two cleaning tools of different functions. Since the cleaning tools are disposed on separate arms and the arms are located outside a wafer, it is difficult to make smaller an apparatus. In addition, during a cleaning operation, the respective arms are moved from one end side of the wafer up to the other end side thereof, a moving distance (moving time) of each arm is long, so that it takes a longer time to process the wafer. As described above, Patent Document 2 and Patent Document 3 are not for cleaning a rear surface of a substrate. Even when these techniques are employed, it is difficult to reduce a size of an apparatus. Thus, neither Patent Document 2 nor 3 can solve the problem of the present invention.